Flu Virus Becoming Resistant to Drug

< Mar. 04, 2009 > -- A new government report shows an increase in resistance to the antiviral drug Tamiflu®. This antiviral drug is primarily linked to influenza A strains, the most common type of flu circulating in the United States.

Last year was the first time Tamiflu resistance was seen anywhere in the world. Almost 100 percent of the influenza A, or H1N1, strain is now resistant to the drug.

This is above the 12 percent increase during last year's flu season, says report author Dr. Alicia Fry, a medical epidemiologist with the influenza division at the US Centers for Disease Control and Prevention (CDC).

"This makes using antiviral drugs very tricky for flu," notes Dr. John Treanor, director of the division of infectious diseases at the University of Rochester Medical Center. "It is more complicated."

"Our message is to get vaccinated with the influenza vaccine", emphasizes Dr. Fry. "The current influenza vaccine has three different virus types in it, and the H1 strain that is in the vaccine is the same strain that is resistant to oseltamivir, or Tamiflu, so the best prevention is still getting the vaccine."

Concern Despite Mild Flu Season

Dr. Neil Schachter, medical director of respiratory care at Mount Sinai Medical Center in New York City and author of The Good Doctor's Guide to Colds and Flu remarks, "We're fortunate in that this is a very mild flu season, and we're not seeing either the numbers of cases or the complications that we normally see in a bad flu season". Yet, "while it is of concern that there are viruses that are developing resistance, it's not all the strains and it's not all the drugs. We're not painted into a corner," he adds.

Many people with the flu are never treated at all, Dr. Schachter points out and reiterates that, "While there's still a flu season out there, everyone should get vaccinated."

Dr. Len Horovitz, a pulmonary specialist with Lenox Hill Hospital in New York City, further explains, "It's not the same as the analogy to bacteria that have developed resistance when they get more virulent. These are natural mutational shifts and drifts, not a result of the overuse of Tamiflu. Just because it's becoming more resistant does not mean that it's a more deadly virus."

A second study found that the Tamiflu-resistant virus still poses a significant health threat to certain groups of patients, in particular those with compromised immune systems who are hospitalized. Both studies were expected to be published in the March issue of the Journal of the American Medical Association (JAMA).

Doctors Respond to the Resistance

In response to the increasing resistance to Tamiflu, the CDC recommends that doctors test suspected flu cases to determine the exact strain of the virus and what medications should be prescribed based on results of these tests.

In the past, two flu drugs were discontinued. In this case, the CDC issued a recommendation against using amantadine and rimantadine in 2006 because of resistant strains of influenza B and H3. However, these drugs work by a different mechanism than Tamiflu and the other drug in its class, Relenza (zanamivir).

In an additional study, researchers in the Netherlands recommended that patients be tested for specific strains of influenza and, if needed, be isolated so as to avoid hospital outbreaks. The authors also cautioned that the conclusions and recommendations were based on only a small number of patients.

Effectiveness of Flu Shot Supported

Pneumonia is a potentially fatal complication of the flu. And, upon further research, the flu shot was determined to be more effective in reducing influenza- and pneumonia-related healthcare visits than the nasal spray form of the vaccine. This finding was based on a third study published in the March issue of JAMA.

The authors of the study, from the Armed Forces Health Surveillance Center in Silver Spring, Md., based their conclusions on an analysis of more than 1 million military personnel over three flu seasons. The flu shot appeared to confer greater immunity than the nasal spray over all three seasons (2004-2005, 2005-2006 and 2006-2007), particularly among soldiers who had been vaccinated in previous seasons.

"Vaccination with either version of the vaccine was protective. Vaccine effectiveness was higher among members receiving an inactivated vaccine shot compared to those receiving intranasal vaccine," study author Dr. Zhong Wang says. "When we look at individuals not immunized during the prior season, vaccine effectiveness became relatively similar between these two groups."

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Facts About Influenza

Influenza, or flu, is a highly contagious viral respiratory tract infection. It can make people at any age ill.

Although most people are ill with influenza for only a few days, some may need to be hospitalized due to the severity. In some cases influenza can lead to pneumonia and death.

Influenza viruses are divided into three types, designated as A, B, and C. Influenza types A and B are responsible for epidemics of respiratory illness that occur almost every winter and are often associated with increased rates for hospitalization and death. Efforts to control the impact of influenza are focused on types A and B.

Influenza type C usually causes either a very mild respiratory illness or no symptoms at all. It does not cause epidemics and does not have the severe public health impact that influenza types A and B do.

Influenza viruses continually mutate or change, which enables the virus to evade the immune system of its host. This makes people susceptible to influenza infection throughout their lives.

Currently, three different influenza viruses circulate worldwide: two type A viruses and one type B virus. Immunizations given each year to protect against the flu contain the influenza virus strain from each type that is expected to cause the flu within that year.

The influenza virus is generally passed from person to person by airborne transmission (i.e., sneezing or coughing). But, the virus can also live for a short time on objects - such as doorknobs, pens, pencils, keyboards, telephone receivers, and eating or drinking utensils.

There are common symptoms of the flu; however, each individual may experience symptoms differently. In most cases, people become acutely ill with several, or all, of the following symptoms:

headache, or severe aches and pains

clear nose, or sneezing

cough, often becoming severe

fatigue for several weeks

sometimes a sore throat, or extreme exhaustion

The symptoms of the flu may resemble other medical conditions. Always consult your physician for an evaluation, a proper diagnosis, and treatment.

The goal of treatment for influenza is to help prevent or decrease the severity of symptoms. Medications to relieve aches, fever, congestion and nasal discharge are often recommended. Bed rest and increased intake of fluids are also suggested.

In some cases, antiviral medications are given as treatment of symptoms or prevention. They can reduce the duration of the disease but cannot cure it. Four antiviral medications have been approved and include zanamivir and oseltamivir.

Vaccine effectiveness varies from year to year, depending upon the degree of similarity between the influenza virus strains included in the vaccine and the strain or strains that circulate during the influenza season.

Mutations can occur in circulating strains of viruses prior to vaccine selection. These mutations sometimes reduce the ability of the vaccine-induced antibody to inhibit the newly mutated virus, thereby reducing vaccine effectiveness.

Although there are many new medications designed to treat flu symptoms and even shorten the duration of the illness, the flu vaccine still offers the best protection against the flu.

The Centers for Disease Control and Prevention (CDC) recommends getting the flu shot every year, between September and mid-November, before the flu season hits (usually December to April). The flu shot takes one to two weeks to become effective.